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26*404b540aSrobert<h1 class="centered"><a name="top">Chapter 25:  Algorithms</a></h1>
27*404b540aSrobert
28*404b540aSrobert<p>Chapter 25 deals with the generalized subroutines for automatically
29*404b540aSrobert   transforming lemmings into gold.
30*404b540aSrobert</p>
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35*404b540aSrobert<h1>Contents</h1>
36*404b540aSrobert<ul>
37*404b540aSrobert   <li><a href="#1">Prerequisites</a></li>
38*404b540aSrobert   <li><a href="#2">Special <code>swap</code>s</a></li>
39*404b540aSrobert</ul>
40*404b540aSrobert
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44*404b540aSrobert
45*404b540aSrobert<h2><a name="1">Prerequisites</a></h2>
46*404b540aSrobert   <p>The neatest accomplishment of the algorithms chapter is that all the
47*404b540aSrobert      work is done via iterators, not containers directly.  This means two
48*404b540aSrobert      important things:
49*404b540aSrobert   </p>
50*404b540aSrobert   <ol>
51*404b540aSrobert      <li>Anything that behaves like an iterator can be used in one of
52*404b540aSrobert          these algorithms.  Raw pointers make great candidates, thus
53*404b540aSrobert          built-in arrays are fine containers, as well as your own iterators.
54*404b540aSrobert      </li>
55*404b540aSrobert      <li>The algorithms do not (and cannot) affect the container as a
56*404b540aSrobert          whole; only the things between the two iterator endpoints.  If
57*404b540aSrobert          you pass a range of iterators only enclosing the middle third of
58*404b540aSrobert          a container, then anything outside that range is inviolate.
59*404b540aSrobert      </li>
60*404b540aSrobert   </ol>
61*404b540aSrobert   <p>Even strings can be fed through the algorithms here, although the
62*404b540aSrobert      string class has specialized versions of many of these functions (for
63*404b540aSrobert      example, <code>string::find()</code>).  Most of the examples on this
64*404b540aSrobert      page will use simple arrays of integers as a playground for
65*404b540aSrobert      algorithms, just to keep things simple.
66*404b540aSrobert      <a name="Nsize">The use of <strong>N</strong></a> as a size in the
67*404b540aSrobert      examples is to keep things easy to read but probably won't be valid
68*404b540aSrobert      code.  You can use wrappers such as those described in the
69*404b540aSrobert      <a href="../23_containers/howto.html">containers chapter</a> to keep
70*404b540aSrobert      real code readable.
71*404b540aSrobert   </p>
72*404b540aSrobert   <p>The single thing that trips people up the most is the definition of
73*404b540aSrobert      <em>range</em> used with iterators; the famous
74*404b540aSrobert      &quot;past-the-end&quot; rule that everybody loves to hate.  The
75*404b540aSrobert      <a href="../24_iterators/howto.html#2">iterators chapter</a> of this
76*404b540aSrobert      document has a complete explanation of this simple rule that seems to
77*404b540aSrobert      cause so much confusion.  Once you get <em>range</em> into your head
78*404b540aSrobert      (it's not that hard, honest!), then the algorithms are a cakewalk.
79*404b540aSrobert   </p>
80*404b540aSrobert   <p>Return <a href="#top">to top of page</a> or
81*404b540aSrobert      <a href="../faq/index.html">to the FAQ</a>.
82*404b540aSrobert   </p>
83*404b540aSrobert
84*404b540aSrobert<hr />
85*404b540aSrobert<h2><a name="2">Special <code>swap</code>s</a></h2>
86*404b540aSrobert   <p>If you call <code> std::swap(x,y); </code> where x and y are standard
87*404b540aSrobert      containers, then the call will automatically be replaced by a call to
88*404b540aSrobert      <code> x.swap(y); </code> instead.
89*404b540aSrobert   </p>
90*404b540aSrobert   <p>This allows member functions of each container class to take over, and
91*404b540aSrobert      containers' swap functions should have O(1) complexity according to
92*404b540aSrobert      the standard.  (And while &quot;should&quot; allows implementations to
93*404b540aSrobert      behave otherwise and remain compliant, this implementation does in
94*404b540aSrobert      fact use constant-time swaps.)  This should not be surprising, since
95*404b540aSrobert      for two containers of the same type to swap contents, only some
96*404b540aSrobert      internal pointers to storage need to be exchanged.
97*404b540aSrobert   </p>
98*404b540aSrobert   <p>Return <a href="#top">to top of page</a> or
99*404b540aSrobert      <a href="../faq/index.html">to the FAQ</a>.
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